Ill] 



THE GROAVTH OF FISHES 



179 



to place, from month to month, and from one year to another. 

 The growth-rate of a fish varies far more than does that of a warm- 

 blooded animal. The general character of the curve remains*, 

 save that the fish continues to grow even in extreme old age, but 

 it draws towards its upper asymptote with exceeding slowness. 



Fig. 45. Growth of cod (after Michael Graham); and of 

 mullet (after C. D. Serbetis). 



The following estimate of the mean growth of North Sea cod is 

 based, by Michael Graham, on a great mass of various evidence; 

 and beside it, for comparison, is an estimate for the grey mullet, 

 by C. D. Serbetis. The shape of the curve (Fig. 45) is enough to 

 indicate that at six years old the cod is still growing vigorously f, 

 while the grey mullet has all but ceased to grow. As a matter of 



* It is essentially an S-shaped curve, as usual; but the conditions of larval life 

 obscure the first beginnings of the S. 



t Norwegian results, based largely on otoliths, are different. Gunner Rollefsen 

 holds that the spawning cod, or skrei, do not reach maturity, for the most part, 

 till 10 or 11 years old, and grow by no more than 1 to 3 cms. a year (Fiskeriskrifter, 

 Bergen, 1933). 



